A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
1. Field of Invention
This invention relates to voltage regulation. The invention is also related to dividing voltage sources. The invention is more particularly related to the division and provision of regulated voltage in microelectronic circuits. The invention is still more particularly related to the provision of capacitor divided voltage provided for power requirements of microelectronic devices, particulary flash memory devices.
2. Discussion of Background
Most electronic systems being designed today use some form of voltage regulation to ensure circuit stability in the face of changes in load current or supply voltage. In addition to being a requisite for proper or stable circuit operation, many times the circuit design can be simplified with resultant cost reductions if it is based on using a regulated supply. Regulated voltage supplies are also useful to provide a voltage level for comparison of other voltages, such as testing charge levels of other devices in an electronic device. The degree of accuracy that the voltage regulator must provide varies considerably with the function performed by the electronics. As a result, there are many different methods for providing the regulation available to the designer.
For many years gas tubes have been used to provide voltage regulation. This is because the characteristic maintaining voltage of these gas discharge tubes remains fairly constant over a relatively wide range of operating currents. Thus, they can absorb any reasonable voltage or current fluctuations occurring in normal operation, keeping the load voltage fairly constant. However, such devices have limited applicability and are not suitable for microelectronic devices.
Solid state voltage regulator diodes or Zeners have been popular since the late 1950""s when they replaced bulky vacuum tubes. Zener diodes primarily serve as voltage regulators with variable operating currents when placed in parallel across a load to be regulated.
Generally speaking, voltage regulation within modern microelectronic devices utilize a voltage source which is regulated based on it""s output. The process is illustrated in FIG. 1. At step 100, an output voltage is sampled. The output voltage is provided from a power supply. At step 110, the sampled voltage is compared to a know value or reference (band gap reference, for example). The reference can be any stable value which provides an indication as to whether the power supply is providing the required or designed power output. Finally at step 120, feedback from the step 110 comparison is fed back into the power supply to adjust the power level output (output voltage). In this manner a regulated power supply is provided.
FIG. 2 illustrates a typical arrangement of electronics for implementing the above described process. A voltage source 200 provides a supply voltage Vsupply. The Vsupply is divided by resistor pair 210,220 to provide a divided voltage 230. The divided voltage 230 is typically divided from the Vsupply to provide a proper voltage level for any connected electronics and a design of the remaining circuit. In this case, the divided voltage provides a voltage for a comparison circuit 250.
The divided voltage 230 is input to the comparison circuit 250 and compared to a reference voltage 240. The comparison circuit 250 is a standard comparator or amplifier configured to produce some difference or adjustment between the divided voltage 230 and the reference voltage 240, producing a feedback voltage 260.
The feedback voltage 260 is then fed back into the voltage supply 200 where it has the effect of either lowering or increasing a voltage level produced, resulting in a regulated power supply. As thus illustrated, the circuit in FIG. 2 performs the method described above for power regulation and also illustrates a method of producing additional specific voltages (divided voltage 230, for example) from a single voltage source using a resistor divider (resistor pair 210,220).
Resistor dividers are common methods for providing specific voltages from a single power source. However, such arrangements require that power is constantly drawn from the voltage source to provide the voltage, and are thus inefficient. One method that does not continuously draw power to provide a divided voltage is illustrated in FIG. 3. A capacitor pair 310,320 is shown that divides a voltage to produce a capacitor divided voltage 330. The capacitor divided voltage is provided to comparison circuit 250 to produce the feedback voltage 260.
The capacitor pair 310,320 are charged up by a voltage source similar to voltage source 200. FIGS. 4A-B illustrates the charge of the capacitors 310,329 charged up from t1 to t2, to provide a voltage level for comparison purposes. Unfortunately, capacitors leak charge (see t2 to t3, for example) or will have charge drawn from them for circuit operation and therefore are unsuitable for stable continuous operations.
The present inventor has realized that continuous current voltage dividers, such as resistor pairs, are unsuitable for modern electronic devices, particularly for on chip devices or pumps that have limited power resources. The present inventor has realized that capacitor dividers are an ideal way to maintain a voltage level for operating purposes within modern microelectronic devices, and that a method of maintaining a charge level in the capacitors without continuous power application would overcome the problems in the prior art.
Roughly described, the present invention provides a nominal power application at predetermined intervals to refresh and maintain a charge level in a capacitor voltage divider circuit. The refresh is performed by calculating an amount of time that a capacitor in the capacitor divider circuit maintains a sufficient charge, and, before that time period has expired, turning the circuit off and reinitializing the capacitors in the circuit, and turning the circuit back on. The timing is generally based on a period of the pump (or voltage supply) and utilizes detailed set of electronics to implement the selected timing regiment.
The present invention is a device that provides a selected voltage level with a minimum of power drain from a supply voltage. The present invention includes a refresh mechanism for initializing capacitor nodes of a capacitor voltage divider circuit to maintain a predetermined voltage division of a voltage source between a capacitor pair of the capacitor voltage divider.
An embodiment of the present invention includes a timing circuit capable of refreshing a capacitor voltage diver circuit at a frequency tied to a frequency of a pump supplying the voltage divider by the capacitor voltage divider circuit.
The present invention can be constructed from parts already present on a microelectronic circuit to implement the timing and functions of the present invention.
The invention may be embodied in either of: a sampling circuit having, a sampling node, and a refresh circuit configured to refresh the sampling circuit at an interval rate of less than an amount of time that charge leakage of the sampling circuit degrades a voltage measurement made at the sampling node beyond a threshold amount; and a regulated voltage supply, having a voltage source, a sampling circuit connected to an output of said voltage source and configured to sample the output without drawing current from said voltage source, and a feedback circuit configured to provide a signal that adjusts an amount of voltage supplied at the output based on the sampled output.
The invention may also be embodied in a method of sampling voltage, comprising the steps of: retrieving a voltage from a divided node of a capacitor divider circuit having a supplied capacitor and a coupled up capacitor, and refreshing the capacitor divider circuit at an interval rate of less time than an amount of time for charge leakage of the capacitor circuit to degrade the voltage retrieved from the divided node. In addition, the invention may be embodied as a set of instructions, stored on a computer readable media, when loaded into a computer, cause the computer to perform the above identified steps; and as a means for performing reinitializing a capacitor voltage division circuit at a refresh rate of less than a predetermined amount of charge leakage occurs in a coupled up capacitor of the capacitor voltage division circuit.